Abstract
The beta decay of the lightest charmed baryon Λc+ provides unique insights into the fundamental mechanism of strong and electro-weak interactions, serving as a testbed for investigating non-perturbative quantum chromodynamics and constraining the Cabibbo-Kobayashi-Maskawa (CKM) matrix parameters. This article presents the first observation of the Cabibbo-suppressed decay Λc+ → ne+νe , utilizing 4.5 fb(-1) of electron-positron annihilation data collected with the BESIII detector. A novel Graph Neural Network based technique effectively separates signals from dominant backgrounds, notably Λc+ → Λe+νe , achieving a statistical significance exceeding 10σ. The absolute branching fraction is measured to be (3.57 ± 0.34(stat.) ± 0.14(syst.)) × 10(-3). For the first time, the CKM matrix element (Vcd) is extracted via a charmed baryon decay as 0.208 ± 0.011exp. ± 0.007LQCD ± 0.001τΛc+ . This work highlights a new approach to further understand fundamental interactions in the charmed baryon sector, and showcases the power of modern machine learning techniques in experimental high-energy physics.